Spark plugs. Why is it so hard?

Kent,
Platinum & Iridium plugs do have benefits, but they act like the 'silent partner'. You don't know they are there working in the background.
Bit of housekeeping first. Both std & specialty plugs have copper cores, which are imbedded in a steel case. I remember hysterical claims, by Champion I think it was, when NGK introduced the copper core that the copper would melt, ya da da....
Now, all the plug makers use copper. Plat, Iridium etc are precious metals & cost more. So there must be a benefit if car makers are willing to spend more on plugs.
There are numerous benefits, even for the hot rodder, most important being ignitability. When the spark is established from a cold metal surface, the phenomenon of electrical quench tries to extinguish the spark. The cold metal tries to absorb the heat, put out the spark. That becomes a misfire, not good for power, economy or emissions. By making the electrode smaller, the chances of quench are reduced. A 2.5mm diam centre electrode has 15 times more surface area than a 0.6mm tip. New problem now: thin steel tip will melt. Hence the use of high melting point metals like Plat & Irid for the centre electrode. Another benefit: less arc over voltage is reqd. From NGK, a 0.040" plug gap with std 2.5mm electrode that needs 21,000v to fire only needs 18,000v with an Irid electrode. That means you run a bigger plug gap with the same ign system; obviously the bigger the spark, the more chance of igniting the AF mixture. A gap that grows due to electrode erosion eventually causes a misfire. Erosion is less with P & I electrodes, so they can be left longer before checking the gap, plus they last longer.